Crates

The crate_type attribute can be used to tell the compiler whether a crate is a binary or a library (and even which type of library), and the crate_name attribute can be used to set the name of the crate.

However, it is important to note that both the crate_type and crate_name attributes have no effect whatsoever when using Cargo, the Rust package manager. Since Cargo is used for the majority of Rust projects, this means real-world uses of crate_type and crate_name are relatively limited.

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// This crate is a library
#![crate_type = "lib"]
// The library is named "rary"
#![crate_name = "rary"]
pub fn public_function() {
    println!("called rary's `public_function()`");
}
fn private_function() {
    println!("called rary's `private_function()`");
}
pub fn indirect_access() {
    print!("called rary's `indirect_access()`, that\n> ");
    private_function();
}
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When the crate_type attribute is used, we no longer need to pass the --crate-type flag to rustc.

$ rustc lib.rs
$ ls lib*
library.rlib